Making a 3D Engine seems to be one of the way of prooving yourself an able programmer....

But...
How does a 3d Engine work...
Im not thinking of making one just yet, but i hope to get a career in games Dev in the future (im currently 15), and so i'd like to know what makes these engines tick.

I can understand that a 1337 3D engine such as Quake III must be blindingly complex to someone who is not involved in the development, but there must be a standard route to creating one?

*How do you start?
*How are shapes (such as maps and levels) imported from files and mapped onto the screen?
*what are 'programs' such as Open GL and Direct Draw, and *what part do they play in the engine (i gather it is a large part!).
*How is memory manipulated so that each pixel does not take up another 40 times as much memory every time "player" "moves" his or her POV within the engine..

Somebody who could please simplify the principles, rules, and methods behind making (even just a simple) 3d engine for me, so i know what im talking about in the future :P

First of all, choose your API. I chose DirectX since I find it very powerful and much more flexible than OpenGL, but thats just me. Secondly, define what game you plan to make with your engine. I build my engine in a way that any type of game can be developed. Will it be a DLL? Make sure you make a strong init function that checks for device capabilities so your engine wont crash later if something is not supported. What kind of features are you planning to include? Maybe a terrain engine or an indoor rendering system too? You should also develop your engine in a way that can be reused for many projects, especially if you are planning to give it away for the public and not only for personal use.
And remember: first make it work and then make it work faster/better. Drawing a triangle on the screen is propably one of the most important things to understand, since all the objects in 3D are consisted of triangles. I hope I helped a bit, for more information, visit http://www.gamedev.com or http://www.flipcode.com which has an extended article about engine architecture. I recomment buying a book on 3D engines, i think it is called "A 3D Engine's Architecture". And read a lot of tutorials, understand them. Some math could help too.
Well, thats it :)